Control apparatus for aircraft



OC- 13, 1953 w. J. MCGOLDRICK CONTROL APPARATUS FOR AIRCRAFT 2 Sheets-Sheet l Filed June 7, 1948 Ctforneg Oct. 13, 1953 w. J. MGGLDRICK CONTROL APPARATUS FOR AIRCRAFT 2 Sheets-Shee 2 Filed June '7, 1948 mi SMS Q, mm

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AfA/s4 sa@ Gttotneg Patented Oct. 13, 1953 CONTROL APPARATUS FOR AIRCRAFT William J. McGoldrick, Edina, Minn., assignor to Minneapolis-Honeywell Regulator Company, Minneapolis, Minn., a corporation of Delaware Application June 7, 1948, Serial No. 31,493

6 Claims.

This invention pertains to automatic steering mechanisms for aircraft which mechanisms are generally known as automatic pilots.

An automatic pilot may be associated with control surfaces of an aircraft which control surfaces are also capable of being manually actuated. Such automatic pilots generally include a responsive device for sensing yaw of the aircraft or Change in heading of the aircraft with respect to its vertical axis and a responsive device for sensing roll and pitch of the aircraft from a datum position. When the aircraft is controlled by the automatic pilot, these responsive devices control the operation of the control surfaces to maintain the aircraft in the datum position. While the control surfaces are manually actuated to alter the position of the craft from datum, the responsive devices. although capable of sensing changes from datum do not control the control surfaces.

If the automatic pilot is connected to the control surfaces after the aircraft is so displaced from datum by the operation of the controls manually, the responsive devices in sensing the change in datum would restore the aircraft to datum despite any desire on the part of the operator to maintain the aircraft in its displaced attitude. To counteract this tendency on the part of the autopilot to return the aircraft to datum, it' has been proposed to oppose the effect of each responsive device in said automatic pilot by a balancing signal while the control surfaces may be manually -actuated so that the automatic pilot is at all times in the state of equilibrium. Therefore, if the automatic pilot be subsequently connected to the control surfaces with the aircraft changed from datum position, this changed position will be automatically maintained by the autopilot.

Instances have occurred, however, when the aircraft was being manually controlled, Where it was desirable to automatically return the aircraft to its datum position. Such instances may arise where the pilot, while manually actuating the control surfaces, has become confused and does not know how to return the aircraft to datum directly. Other instances may develop where the operator of the control surfaces is suddenly aware that he is becoming disabled for further operation of the control surfaces. The operator in sensing his condition anticipates that he will not be able to return the aircraft to datum position To provide for the above and similar contingencies, it is an object of my invention to provide an improved automatic steering mechanism for an aircraft which may be connected to the control surfaces of said aircraft while the aircraft is in any one ofV various attitudes and which mechanism will maintain the aircraft in said attitude. However, this mechanism also includes a manually operable controller which may be operated in an unlimited or unprecise manner for automatically effecting return of the aircraft to a datum position irrespective of the current attitude of the aircraft.

It is a further object of my invention to provide such steering mechanism with manually adjustable control devices for altering the attitude of the aircraft through said mechanism about a plurality of axes but which devices as adjusted are rendered ineective in said mechanism upon operation of said manually operable controller whereby the attitude of the aircraft is restored to a predetermined attitude.

The above and further objects of my invention will appear upon consideration of the following description and drawings illustrating a preferred embodiment of my invention.

In the drawings: Figure 1 is a diagrammatic arrangement of the association of operative parts of my steering mechanism during automatic control of an aircraft.

Figure 2 illustrates a portion of the steering mechanism associated with the operation of the rudder of an aircraft whereby the rudder power means may be connected or disconnected from said rudder.

Referring to Figure 1, there is illustrated therein an automatic steering mechanism for an aircraft having an aileron control for regulating the movements of the aircraft about the roll axis, a rudder control for regulating the movements of the aircraft about the yaw axis, and an elevator control for regulating the movements of the aircraft about the pitch axis. The aileron control includes main aileron cables lil which are connected to ailerons not shown of the aircraft. The opposite ends of the cables lo "nay as is conventional lie in separate grooves of a double grooved pulley Il and may be secured therein to the pulley. The pulley Il is iixed to a shaft l2 which may be suitably mounted in bearings carried by the aircraft. A manually operable control stick, a portion I4 of which is shown, is carried by the shaft l2. It will be evident that upon rotation of the shaft l2 by the rocking of the stick I4 from one side to the other that the main aileron cables I0 may actuate the ailerons in wel] known manner. In the present arrangement as in similar automatic steering mechanisms, control of an aircraft is effected by operating the ailerons, rudder, and elevator. The operation is accomplished by motor or power means. Power operation of the ailerons is effected by cables i5 which extend from a servomotor cable drum i5. One cable l5 extends from the drum i5 through a guide pulley |'i to a suitable clamping means is which secures it to one main aileron cable i. The opposite cable l5 extends from drum I6 and through a guide pulley l to a suitable clamp which secures it to the other aileron cable lli. Cables it may alternatively by operated by a manually operable control stick pivoted on axis l2. The cable drum l5 is carried by a servomotor shaft 2| operated by servomotor 22. The servomotor 22 is controlled by an amplifier 25. The amplier 25 is provided with power input leads 25 and 2l connected to a suitable source of alternating current such as an inverter (not shown) The amplifier 25 is also provided with signal input connections 25 and 25. The direction of rotation of servomotor 22 depends upon the phase relationship between the alternating voltages across signal input terminals 25, 29 and across the power input connections 25, 2l. The amplifier-servomotor combination may be of the type disclosed in an application of Willis H. Gille, 447,989, filed June 22, 1942.

The signal input leads 28, 29 of amplifier 25 are connected to a balanceable control circuit comprising variable impedance network 38, lead d6, variable impedance network lll, lead 54, variable impedance network 5i, lead 69, variable impedance network "iii, lead il to ground, and to grounded lead 29 of amplifier 25.

The variable impedance network consists of a servo-balance potentiometer 5|, an automatic recovery potentiometer 35, a voltage dividing potentiometer 35, and a transformer 2|. Potentiometer 2| includes a resistor 32 which is connected across the ends of a secondary winding 42 of transformer dil. Potentiometer 3| includes a wiper which is operated from the servomotor shaft 2| through a suitable operating connection 5ft. The voltage dividing potentiometer 38 has a resistor 59 which has one end connected to wiper 35 of potentiometer 3| and has its other end connected in series with a loading resistor 45 to a center tap il of secondary winding d2 of transformer di. Potentiometer 33 includes a manually adjustable tap :it which is connected to lead 28 extending from amplifier 25. Potentiometer 35 has a resistor 35 which is connected across the ends of secondary winding d2 in parallel with resistor 52 of potentiometer 3|. A wiper 3l of potentiometer 35 may be manually adjusted over the surface of resistor 36. Transformer 5| includes a primary winding d3 which may be connected to the suitable source of alternating current.

impedance network il consists of a centering potentiometer d8 and a transformer 5|. A resistor 2S of potentiometer d5 is connected across the ends of a secondary winding 52 of transformer 5i. Potentiometer te includes an adjustable wiper 52 which may contact the surface of resistor iis. The wiper 5t is operated either manually or by means of a centering motor 52A to be described. Transformer 5| includes a primary winding 53. Lead filextends from wiper 3l of potentiometer 35 to a center tap of secondary winding 52 of transformer 5|.

Impedance network 5l consists of a directional gyro aileron potentiometer 53, a vertical gyro roll axis potentiometer' 5|, and a transformer 6-5. Potentiometer 55 includes a resistor 59 which is connected across the ends of a secondary winding 5S of transformer 55 and a wiper 5) movable over the surface of resistor 55 and operated from a deviation responsive device illustrated as a directional gyro 55. The directional gyro 55 which will be described later operates the wiper 55 With respect to resistor 53 in proportion to the deviation of the aircraft from a desired heading. The potentiometer 5| consists of a resistor 62 whose ends are connected across the ends of secondary winding 56 in parallel with resistor 59- and a wiper 55 which is operated through a suitable connection E@ from a vertical gyro to -be described. Transformer 55 is indicated as having a primary winding i3 which is common to the transformers lll and 5|. Lead 54 extends from wiper 56 to wiper 65 of the directional gyro aileron potentiometer 58.

Impedance network 'it consists of a turn control potentiometer '12 and a transformer il. Potentiometer 'l2 has a resistor i3 which is connected across the ends of a secondary winding 18 of transformer ii and a manually adjustable wiper 'id which is operated by the manually operable turn control knob i5. Transformer Tl includes a primary winding 53 which is common to the transformer 5| of network d?. Lead B9 extends from wiper 53 of potentiometer 6| to wiper iii of potentiometer i2. Lead '5| extends from a center tap of secondary winding 'I8 of transformer 'if to ground. The return to the amplifier is through grounded lead 29 connected thereto.

The rudder not shown of the aircraft may be operated from cables H!) extending from a, manually operable rudder bar which is pivoted at l2 to the aircraft. Power operation of the rudder bar i may be effected by cables I |5 extending from a servomotor cable drum |5. The drum ||5 is carried by a shaft |2| which is driven by servomotor |22. The servomotor |22 has its operation controlled by an amplifier |25. The ampli- -f er |25 and the servomotor |22 may be identical with the amplifier 25 and the servomotor 22 of the aileron control. Power input terminals |26, i2? or amplifier 525 are connected to the suitable source of alternating voltage. Amplifier |25 is provided with signal input terminals not shown which are connected to input leads |23, |29. The direction of rotation of servomotor |22 depends upon the phase relationship between the voltage across the input leads i253, |22: and the voltage across power input leads |25, |21. An input control signal circuit comprising a balanceable network extends from lead |28, variable impedance network 35, lead |125, variable impedance network ifi?, lead i563, variable impedance network |55, lead |75, voltage dividing potentiometer |16, lead |59, variable impedance network l', lead 'il to ground, and to the grounded lead |29 ofanpliner |25. Y

The impedance network |36 includes a servobalance potentiometer I3 I, van automatic recovery potentiometer |35, a voltage dividing or trimmer potentiometer |35, and a transformer Mi. Potentiometer |3| includes a resistor |32 whose ends are connected across the ends of a secondary winding i452 of transformer MI, Potentiometer i3! includes an adjustable wiper |33 which contacts the surface of resistor |32 and is operated through a suitable connection |34 from the servomotor shaft |2|. The automatic recovery potentiometer |35 has a resistorA |36 whose ends are connected across thel ends of secondary winding |42 in parallel with resistor |32 and a manually adjustable wiper |31 which contacts thev surface of resistor |36. Trimmer potentiometer |38 has a resistor |39 having one end connected to wiper |33 of potentiometer |3| and having its other end connected in series with a loading resistor |45 to a center tap |44 of secondary winding |42. A manually adjustable tap |40 of potentiometer |38 is connected through lead |28 to amplifier |25. The transformer |4|` consists of the secondary winding |42 and a primary winding 43.

Variable impedance network |41 consists of a centering potentiometer |48 and a transformer |I. Potentiometer |48 has a resistor |49` whose ends are connected across the ends or a seccndary winding |52 of transformer |5l. Potentl'ometer |43 includes a wiper |50 which contacts the surface of resistor Idil and the point of contact may be Varied by manually operating the wiper |53 or operating it from a centering motor 52B. which is similar to centeringmotor 52A of the aileron control. Transformer |5| includes a primary winding 53. A lead |4 extends from wiper |31 of potentiometer |35 to a center tap of secondary winding |52 of transformer |5|.

Variable impedance network |55 includes a yaw rate gyro potentiometer |55, a directional gyro rudder potentiometer |60, a Voltage dividing or trimmer potentiometer |65, and a transM former |1|. Potentiometer |55 has a resistor |51 whose Vends are connected across the ends of a secondary winding |12 of transformer |1| and a` wiper |58 which maybe operated over the surface. of resistor |51. Operation of wiper |58 is effected by a yaw rate gyro |59. The rate gyro |59 measures the angular speed of the aircraft about the Vertical or yaW axis. This ayro |59 is of the conventional type whose rotor is mounted with two degrees of angular freedom and which movement is further restricted about one axis by spring restraining means. The gyro 59 may be similar to the gyro disclosed in United States Patent 2,190,390 for measuring the angular speed about the normal axis. Potentiometer |60 has a. resistor |6| which has its ends connected across the ends of secondary winding |l2 in parallel with resistor |51 and a wiper |52 which may be operated over the surface of resistor |6l by an operating connection |53 extending from directional gyro 55. Potentiometer |55 has a resistor |66A having one end connected to wiper |58 of the rate gyro potentiometer |56 and hav ing its other end connected to a center tap |14 or secondary winding |12 of transformer |1|. A manually adjustable tap |61 of potentiometer |65 is connectedby means of lead |54 to the wiper |50 of centering potentiometer |48. The trans-Y former |1| consists of the secondary winding |12 and a primary winding 43.

Voltage dividing potentiometer |15 has a red sistor |11 and an adjustable tap |13. One end of resistor |11 is connected to center' tap 51 of secondary Winding 66 of transformer 5E of network 51 and the other end of resistor i-l'i is connected tov wiper 63 of the vertical gyro aileron potentiometer 5|. A lead |15 extends from adjustable tap |18 to wiper |62 of the directional gyro rudder potentiometer It.

The remaining impedance network lll of the input control circuit of amplier |25 is common with the input control circuit of amplifier 25 and has been previously described in connection therewith. To complete the rudder ampler signal circuit, lead 69 extends from wiper 63 of the vertical gyro aileron potentiometer 5| to wiper 14 of the turn control potentiometer 12, and lead 1| extends from a center tap of secondary winding 18 to ground and through ground to input connection |29 of amplier |25.

Control of the aircraft about the pitch or transverse axis is obtained from an elevator 20S carried on a shaft 238 suitably journaled in the aircraft. The elevator 259 may be operated by means of an arm 261 carried on shaft 2-38 which arm has its free end connected to one end of a link 2| e. The opposite end of link 2| is pivoted to the lower end of a manual control stick 2|4. Thev manual control stick 2 5 is carried by a shaft 2|2 suitably journaled in the aircraft for fore and aft movement.

Power operation of the control stick 2|4 is effected by cables 2|5 extending from an elevator cable drum 2|5. The cable drum 2|5 is carried by a shaftY 22| driven by an elevator servornotor 222. The operation or servomotor 222 is con trolled by an ampliier 225. Amplifier 225 has power input leads 225, 22! connected to the source of alternating voltage. Amplifier has. control signal input leads 228, 22d connected to an input control circuit. The direction of rotation of servomotor 222 depends upon the phase relationship between the voltage across input lead 228, 229 and the voltage across the power input leads 225, 221. IThe amplifier 225 and servomotor 222 may be similar to the amplifier 25, and servornotor 22 of aileron control.

The signal control circuit of ampiiiier 225 con stitutes a balancealele network and extends from lead 228, impedance network 23d, lead 246, impedance network 2li?, lead 25d, impedance nete work 256, lead 2id, to ground and 'to grounded connection 225 of amplilier 225.

The variable impedance network 23e consists of an elevator servomotor balance potentiometer 23|, an automatic recovery potentiometer 235, a voltage dividing or trimmer potentiometer 233, and a transformer 24|. Potentiometer 23| has a resistor 232 whose ends are connected across the ends of a secondary winding 252 of trans former 25| and a wiper 233 which is operated through a siutable operating connection 23d from the servomotor shaft 22|. Potentiometer' 235 has a resistor 235 which is connected across the secondary winding 2&2 in parallel with the resistor 232 and a manually adjustable wiper 231. Potentiometer 233 has a resistor ually adjustable tap 228. 239 is connected to wiper 233 of potentiometer 23| and the opposite end of resistor 235 is connected in series with a loading resistor 245 to a center tap 254 of secondary winding 2d2. Lead 228 extends to the wiper Transformer 24|, in addition to the secondary winding 2552, includes the primary winding d3.

Variable impedance network 241 consists of a centering potentiometer 243 and a transformer 25|. The potentiometer 248 has a resistor 249 whose ends are connected across a secondary winding 252 of transformer 25|. The potentiometer 248 includes an adjustable wiper 250 which may be manually adjusted over the resistor 249 and may also be adjusted by a centering motor 52E similar to the centering motor 52A of the aileron control. A lead 246 extends from wiper 231 of the potentiometer 235 to a center tap of secondary Winding 252. The transformer 25| in addition to the secondary winding 252 includes the primary Winding 53. Variable impedance se and a man- One end or resistor network S consists of a vertical gyro roll axis up elevator potentiometer 251, a voltage dividing or trimmer potentiometer 215, a variable resistor 260, a vertical gyro pitch axis potentiometer 234, and a transformer 218. Potentiometer 251 has a resistor 252 one end whereof is connected to one end of a secondary winding 219 of transformer 213. The opposite end of resistor 258 is connected in series with the variable resistor 233 to the opposite end of secondary winding 219. Potentiometer 251 includes a wiper 259 adjustable over the surface of resistor 253 by means of an operative arrangement 233 driven from the operative connection 64 extending from the vertical gyro 219. Vertical gyro 2113 is of the type well known in the art having a rotor mounted for rotation about a vertical axis. The gyro 213 is ,similar to the gyro horizon K of United States Patent 2,190,390. The operative connection 94, like the arm 4 of the aforesaid patent, measures the bank of the aircraft.` The operative arrangement 233 transmits motion. from connection 34 to wiper 259 and is so constructed that irrespective of the direction of bank of the aircraft the wiper 259 is moved in the same direction or to the left in Figure 1. The potentiometer 215 consists of a resistor 211 having one end connected to wiper 259 and having its other end connected to the junction between resistor 253 and the variable resistor 233. The potentiometer 215 has a manually adjustable tap 213 which has a lead 254 extending therefrom to wiper 259 of the centering potentiometer 248. Variable resistor 269 consists of a resistor 262 and an adjustable tap 291. Potentiometer 234 consists of a resistor 235 which is connected across the secondary winding 219 of transformer 218 and an adjustable wiper 236 which may contact the surface of resistor 265 and which is driven through a suitable operating connection 253 from the vertical gyro 211). The vertical gyro 219 is so arranged in the aircraft that upon movement of the aircraft about the pitch or transverse axis the wiper 266 is displaced with respect to its resistor 265. Lead 214 extends from wiper 253 to ground. Transformer 218 consists of the secondary winding 219 and primary winding 43. l

in Figure 2, there is shown apparatus which is associated with the rudder control channel of the automatic steering mechanism illustrated in Figure 1. Parts of the arrangement illustrated in Figure 2 are duplicated in the aileron and elevator control channels of Figure 1, other parts shown in Figure 2 are common to the aileron and elevator control of Figure 1, and others are associated only with the rudder control channel. The relationship of the parts of the arrangement shown in Figure 2 to these three categories mentioned will be subsequently stated.

In Figure 2, a source of D. C. voltage illustrated as a battery 388 through a two position, closed or open, master button switch 499 supplies D. C. Voltage to amplier relays 3119, 310. The relays 394i, 319 are contained within the ampliers 25, 125, 225 of Figure 1 as disclosed in the aforesaid application and are alternatively operated in accordance with the phase relationship of the signal input voltage to the power input voltage. Amplifier relays 399, 319 may alternatively control a centering motor 52B. or a servomotor 122 through a rudder engaged relay 320. A master engage relay 344 controls the energizaton of rudder engage relay 329. The energization of master engage relay 344 is controlled by a circuit including several series connected parts comprising master button switch 400, a normally closed, momentarily opened main disconnect switch 316, anti-engage relay 359, and normally open momentarily closed main engage button switch 354. The master engage relay 344 is also controlled by an automatic recovery relay 31|. The automatic recovery relay 319 is controlled by a circuit including several series connected parts comprising master button 409, main disconnect switch 316, and normally open, momentarily closed automatic recovery button switch 384. A normally closed, momentarily opened rudder disconnect switch 339 controls the deenergization of rudder relay 329.

A directional gyro 55 is controlled by a caging mechanism 419. The energization of the caging mechanism 419 is controlled by a caging relay 415. The caging relay 415 is controlled alternatively by the rudder engage relay or by a turn control knob 15 through the automatic recovery relay 319. A transformer 441 is controlled by the automatic recovery relay.

With this brief statement of the interrelationship of the components of Figure 2, the details of the components will be considered. The master button switch 4911 comprises two spaced contacts 432, 493 and an operable two position bridge member 431 coacting therewith. The amplifier relay 369 comprises an energizable coil 391 which is energized from a source disclosed in the aforesaid application of Willis l-I. Gille. The coil operates a plunger 3112 carrying a switch bridge member 333 which coacts with spaced contacts 394, 395. When the relay is unoperated, the bridge member 3113 does not engage the contacts 394, 395. Amplier relay 319 includes an operating coil 31 1 which is energized from a source as disclosed in the aforesaid application. The coil 311 operates a plunger 312 which carries a switch bridge member 313 which coacts with spaced contacts 314, 315. When the coil 311 is unenergized, the bridge member 313 does not engage contacts 314, 315.

The centering motor 52B is areversible D. C.

f motor having permanent magnet field poles 349 and a wound armature 341. Connected across the armature 341 is a center tapped resistor 342.

The servomotor 122 may be of the type disclosed in the aforesaid Gille application and such servomotor as disclosed therein is provided with brake energizing windings and clutch operating windings, the latter providing reversible rotation of the servomotor. Until the brake windings have been energized, the servomotor is not operatively associated with its control surface.

The rudder engage relay 329 includes an operating winding 321 and coacting plunger 322. The plunger 322 is operatively connected to four pivoted switch arms 323, 324, 325, and 323 which switch arms individually constitute the movable part of a single-pole double-throw switch. In normal position, the armature 322 is in the upper position as shown at which time the coil 321 is unenergized. Switch arm 323 coacts with a lower engage relay holding circuit contact 334 and with an upper caging relay contact 333. Switch arm 324 coacts with a lower, servomotor brake winding contact 332 and an upper, idle contact 331. Switch arm 325 coacts with a lower, servomotor one rotation clutch contact 331] and with an upper, one rotation centering motor contact 329. Switch arm 325 coacts with a lower, servomotor opposite rotation clutch contact 328 and an upper, opposite rotation centering motor contact 321.

Master engage relay 344 includes an operating coil 345 and a plunger 346. The plunger 346 is operatively connected to single-pole single-throw switch arms 341, 348, and 349. The switch arms 341, 348, and 349 are electrically connected to a common bus bar 350. Switch arm 341 coacts with a contact 35| which is electrically connected to a holding contact in the elevator engage relay not shown similar to contact 334 of the rudder engage relay. Switch arm 348 coacts with contact 352 which is electrically connected to a holding circuit contact for the aileron engage relay not shown similar to contact 334 in the rudder engage relay. Switch arm 349 coacts with contact 353 which is electrically connected to contact 334. In normal position the switch arms 341, 348, and 349 do not contact their respective contacts 35|, 352, and 353 at which time the coil 345 is unenergized.

Main disconnect switch 3|6 comprises a push button operated automatically released bridge member 3|1 which coacts with space contacts 3 I8, and 3 9.

The anti-engage relay 359 is provided with an operating coil 360 and a plunger 36| coacting therewith. 'I'he armature 36| is operatively associated with a switch arm 362 of a single-pole single-throw switch. The switch arm 362 coacts with main engage control Contact 356. @ne end of coil 360 is connected to a bus bar having terminals 353, 354, and 395. Terminal 355 is designated the rudder centering motor contact. Terminals 364 and 363 are identified as the aileron and elevator centering motor contacts respectively.

The main engage button switch 354 comprises two space contacts 355, 356 with which coacts a manually operated automatically released bridge member 351.

The automatic recovery relay 310 is provided with an operating winding 31| and a plunger 312 coacting therewith. Plunger 312 is operatively connected to pivoted switch arms 313, 314, and 315 of three single-pole double-throw switches. Switch arm 313 coacts with a lower, automatic recovery relay holding circuit contact 38| and an upper, turn control contact 380, Switch arm 314 coacts with a lower, master engage relay contact 319 and an upper, idle contact 313. Switch arms 313 and 314 are electrically connecte-d by a lead 382. Switch arm 315 coacts with an upper, transformer energizing contact 316 and a lower, transformer deenergizing and ground contact 311. In normal position the plunger 312 is in the upper position as shown with the coil 31| deenergized.

The automatic recovery switch comprises two spaced contacts 365, 386 and a push button operated automatically released bridge member 351 which coacts with the contacts. The rudder disconnect switch 399 may be of the push button normally closed momentarily open type and coniprises spaced contacts 39|, 392 and a bridge member 393 which coacts with the contacts.

The directional gyro 55 is of the type Well known in the art having a rotor, not shown, supported for rotation about a horizontal axis within casing 404. The casing 404 in turn has trunnions 409 for supporting it Ion a horizontal axis at right angles to the spin axis of the gyro rotor. The trunnions are carried in an outer gimbal ring 405. The outer gimbal ring 405 is pivoted about a vertical axis by means of its trunnions 406, 401 which are carried by suitable bearings supported by the craft. Projecting from one end of casing 404 is an extension 408 which constitutes part of a caging mechanism to be described. The directional gyro is so mounted in the aircraft that upon changes in heading of the aircraft about the yaw or Vertical axis the gyro moves with respect to the craft about the vertical axis of the outer girnbal ring 405. This movement is transmitted through the operative connection |33, Figure 1 to wiper 60 of the directional gyro aileron potentiometer 5S and to wiper |32 of the directional gyro rudder potentiometer |69.

The caging mechanism 4|0 may consist of two alternatively energizable operating coils 4I l, H2 and an armature 4|3 which coacts therewith. The armature 4|3 carries at one extremity a hollow conical shaped member 4| 4 which may be engaged with the projection 408 of gyro casing 404. The armature 4|3 is supported for longitudinal movement by any suitable means not shown. The coil 4|2 is designated the caging coil and the coil 4| the uncaging coil. Upon the energization of coil 4|2 the armature 4| 3 is moved 'to engage the conical shaped member 4|4 with the projection 408 whereby the gyro rotor is centered and caged. Upon the operation of coil 4| l the armature 4|3 is moved to disengage the cone 4| 4 from the projection 408.

The caging relay 4|5 consists of an operating coil 4|6 and a plunger 4|1 coacting therewith. The plunger 4|1 is operatively connected to a switch arm 4|8 of a single-pole double-throw switch. When the master button switch 459 is unoperated as shown, the switch arm M8 of the caging relay is in the lower position when the coil 416 is unenergized. Switch arm d l coacts with a lower, uncage contact 420 and an upper caging contact 4 I 9.

rIhe turn control knob 15, in addition to operating the wiper 14 of the network 16, Figure l, also operates a switch arm 423 of a switch 422. Switch 422 includes two spaced contacts E25 which may be pivoted at their lower ends and are electrically connected together. The switch 423 is interposed between the spaced contacts 424, S325. A transformer 44| is provided with a primary winding 53 and several secondary windings 52, 52, 252, and 18 as shown.

While features pertaining to the rudder control only have been illustrated in Figure 2, it is to he understood that the servomotor, centering motor, the individual disconnect switch, the ampliiier relays, and the individual engage relay are duplicated in the aileron control channel in the elevator control channel. The features illustrated in Figure 2 which are common to the aileron, rudder, and elevator channels are the main engage switch 354, the master engage relay the automatic recovery switch 3224, the automatic recovery relay 310, the main disconnect switch SiS, the master button switch and the anti-engage relay 359. The features shown in Figure 2 which are confined solely to the rudder control channel are associated with the caging contact 333 of the rudder engage relay in the aileron and elevator engage relays, the contacts corresponding with contact of the rudder engage relay 529 are idle. In other words, the rudder engage relay 32S is the only relay of this type which controls the caging relay c and the caging mechanism 4|0.

Operation Having described in detail the component parts of the automatic steering mechanism and their interrelationship, the operation of the steering system wil lbe described. It is now apparent at the aileron, rudder, and elevator control annels of Figure l each include an amplier which is controlled by a network. Referring to the rudder control channel of Figure 1, the control network as stated is made up of variable impedance networks |30, |41, |55, a portion of network 51 modied, and network 13. In network i3d if wiper |33 is at the electrical center of resistor |32 and wiper |31 is at the electrical center of resistor |39, wiper |33 and wiper |31 at the same potential and no signal will therefore be generated in network |33. In network |41 if wiper |53 be at the electrical center of resistor |49 there will be no potential diiference between wiper |50 and the center tap of secondary winding |52, therefore network |33 will not generate any output signal voltage. Similarly, in network |55 if wiper |58 is at the electrical center of resistor |51 and wiper |32 is at the electrical center of resistor 16| wipers i558 and |52 will be at the same potential and network lE will not generate a signal. In network 51, if wiper '53 be at the electrical center of resistor 52, the wiper 33 will be at the same potential as center tap 61 of secondary winding and no signal voltage will be supplied to the potential divider |16 and therefore the rudder control network will not be supplied with a signal voltage from network 51. Similarly, if the turn control operated wiper 14 be at the electrical center of resistor 13 the wiper 1li will be at the potential of the center tap of secondary winding i3 and therefore the turn control potentiometer i@ will not generate a signal voltage. Since it is evident that the various impedance networks recited are connected in series and since they do not generate signal voltages under the conditions described, the input circuit of amplifier |25 is in balanced condition.

The rudder control network may become unbalanced due to the change in attitude of the aircraft about its axes. For example, if the aircraft changes position about its yaw or vertical axis, the directional gyro 55 through the operating connection |63 will adjust wiper |t2 with re spect to resistor'li resulting in a signal voltage being generated in network |55 to cause unbalance of the input circuit of ampliner |25. Also, if the aircraft moves about its longitudinal or roll axis, the vertical gyro 21d will respond to I this movement and through the operating ccnnection te will adjust the wiper 53 with respect to resistor E2. This movement of wiper [i3 will change its potential with respect to center tap fil of secondary winding 5S. The potential difference between the wiper 63 and center tap t? will be applied across the voltage dividing resistor |11 and tap |13 may be positioned to select any desired portion of this potential difference. rEhe input circuit of amplifier |25 is thus also unbalanced upon movement of the aircraft about the roll axis.

The rudder control network is rebalanced autornatically by controlling alternatively two networks !33 or I4?. When the automatic steering control system is not controlling the aircraft, the rudder control network is automatically balanced by the operation of centering motor 52H. When the automatic steering mechanism is not controlling the aircraft as stated, the rudder engage relay 32@ is in the position shown in Figure 2. If the rudder control network be now unbalanced the amplifier |25 will operate to cause the operation of either relay 300 or relay 3H?. If ampliiier relay 300 be operated due to the unbalance of the network of amplifier |25, a circuit is completed from battery 388, operated master button 453|?, lead 442, contact 3&5, bridge member 333, contact 354, switch arm 32, contact 325, through reversible steering motor 32B., resistor 342, lead 443, anti-engage relay coil 33t, to ground and to the grounded side of battery 388. The steering motor 52B. operates the wiper |53 of the centering potentiometer |48 until the rudder input circuit network is in balanced condition. As long as the input circuit is unbalanced, the centering motor EER will continue to operate and the anti-engage relay 359 will be energized to disengage switch arm 352 from its contact 35d.

In the elevator control channel and the aileron control channel, the balanceable networks con-z trolling respectively ampliers 225 and 25 operB ate in a manner similar to that for amplifier |25 described. Since the elevator and aileron centering motors complete their circuits through terminals 353 and 384 and coil 3S@ of the antiengage relay, it is evident that the switch arm it is disengaged from contact as long as either of the three control channels are in unbalanced condition.

The aircraft may now be conditioned for the attitude it is to assume on automatic recovery. The aircraft, for this purpose, may be manually operated until it is in the desired attitude. The automatic recovery button 381 may now be operated to bridge contacts 38E, 386. A circuit will now be complete from battery 338, master button 43B, main ous bar 444, main disconnect switch 3|?, lead M5, automatic recovery switch 3th?, lead 445, automatic recovery relay winding 31| to ground and to battery ground 45.8. Operation of the automatic recovery relay 313 energizes the master engage relay 344 from a circuit extending from battery 38S, master button 493, main bus 444, main disconnect 3|1, lead 445, lead 443, switch arm 313, lead 332, switch arm 3M, contact 319, lead 45t, lead 45|, winding 345 of relay 344 to ground and to battery ground 445.

i A holding circuit for winding 3H of the automatic recovery relay 31e is also completed from energized lead 44S, switch arm 313, contact 38 l, winding Sli, to ground and to battery ground 4423. The operation of the automatic recovery relay 315i also disconnects the primary winding 53 of transformer #54| from its energizing circuit comprising lead 453, contact Sit, switch arm 315, and causes the input side of primary winding 53 to be connected to ground through switch arm 315, and contact 311 whereby the transformer 44| is deenergized. The secondary windings associated with transformer 34| therefore are no longer energized.

The operation of the master engage relay 344 causes the switch arms 349, 348 and 341 to engage their respective contacts. A circuit is now completed from energized lead 445, lead 452, bus bar 35B, switch arm 349, contact 353, lead 454, relay winding 32|, rudder disconnect switch 389, to ground and to battery ground 448. The rudder engage relay 32@ is thus energized. A similar circuit as is now evident is provided for the aileron and elevator engage relays.

The operation of the rudder engage relay 32B causes the switch arms 323, 324, 325, and 32E thereof to engage their lower contacts. A holding circuit for coil 32| is now provided from energized lead 452, switch arm 323, contact 334, coil 32|, rudder disconnect switch 383, to ground and to battery ground 448. The disconnection of switch .arm 3.23 from .contact 333 deenergizes fthe caging relay 4|5 whereupon the armature lll moves to the position shown wherein switch arm 41B engages contact 420. The .cagingmechanism is thereby energizedto uncage kthe .directional gyro. The circuit for .energizing `the caging mechanism extending from energized lead v1142i, lead 455, switch Varm 4.|8, contact 420, to the nnca'ging coil Ml., to ground and to battery ground 43.

`The .engagement of switch arm 324 with 'lower contact 332 of the :rudder .engage vrelay 320 com pletes a circuit through a lead similar to .lead |82, Figure :2, of the aforesaid Gille application to energize the brake lwindings 450, 46| to place the rudder servomotor |22 in .braked condition with .respect to the rudder .of 'the aircraft whereby said servomotor is associated with said rudder. Ihe .engagement of switch arm 325 with its lower contact 330 joins the rudder amplier .relay 3|@ with one clutch `coil |62 .of the rudder vservo E22 corresponding with electromagnet |54 in the aforesaid application to permit operation of said servo. The-engagement of switch arm 325 with its lower contact 328 joins the amplier relay 3GB tion and the craft is in a condition for auto- ,i

matic control. Should the .aircraft change its attitude from that in which .it was placed prior to `the operation of .the automatic recovery button 381 the attitude with respect to .each axis may be regained by the manual adjustment of the individual automatic recovery potentiometers 35, |35, and 235.

With the aircraft again in its desired attitude, the lautomatic control may be .disassociated from the control surfaces by the operation of the main disconnect switch button 311 to open the circuit across the contacts 313, sl. The operation of the main disconnect button 3.!1 will deenergize the automatic recovery relay lwinding 31| and the master engage relay winding 345 and the rudder, aileron, and elevator relays to transfer the rebalancing of the aileron, rudder, and elevator networks from the .servomotor rebalancing potentiometers 3|, |3| and 23| to the centering potentiometers 58, |48 and248.

.Having estaiblished a desired attitude of the aircraft for automatic recovery lthe aircraft may be manually or automatically controlled to fiyzas desired. The operation of the .automatic recovery arrangement will be considered when the pilot desires that the yaircraft regain va predetermined attitude from which it .had departed through the operation of the control surfaces manually. When the pilot manually effects changes in the attitude of the aircraft about the vroll and pitch axes, the vertical gyro responds as stated to such changes and operates wiper 63 of potentiometer B I in network .51, wiper 259 lof the up-elevator potentiometer .251., and wiper 266 of the pitch axis potentiometer 264 whereby the aileron, rud- 14 der., and elevator networks are unbalanced. As described previously, the centering motors respectively maintain their networks in a balanced condition when the plane is manually flown.

When the pilot wishes to regain the .desired attitude of :the aircraft while under manual control, he operates the automatic recovery button 331 which associates the respective servomotors with their lcontrol surfaces and places the servomotor under .control of its amplifier. The opening of the circuitto primary winding 53 vof transformer 44| disables centering potentiometers 48, 4|118 and 24u, the now unoperated turn control potentiometer TF2 with respect to supplying a control in thei respective networks.

The datum or base for each control network now changes from the centering potentiometers in each network to the automatic recovery potentiometers in the .respective networks. This change in the base yor datum from the centering potentiometers .to the automatic recovery potentiometers in the several networks causes a signal to be applied to their ampliers when the plane is in the attitude achieved by manual control. For example, if the aircraft is in a banked turn, 'the vertical gyro 210 will have provided a signal in the aileron, rudder, and elevator control networks which will have been balanced by the centering potentiometers. The change from the centering 'potentiometer base to the automatic recovery potentiometer base results in a vertical gyro signal .in each network which is unbalanced.

lThe amplifiers 215, |25, and 225 operate in response to this vertical gyro .signal and cause the aileron, rudder, .and elevator servomotors to operate their control surfaces .and also operate their follow up wipers 33, 33, and 233 to rebalance the several networks. The control surfaces are moved in such a direction as to correct for the condition which resulted in the vertical gyro signal. Yills the aircraft moves toward its desired attitude, the vertical gyro signal decreases result ing in en unbalance of the .several networks in the .opposite direction Aso that the amount of control surface displacement is decreased. When .the signal from vertical gyro 21B is reduced to zero at which time the aircraft has regained its desired lattitude the control surfaces have been moved back to their normal position.

The :directional gyro 55 and the rate gyro |59 will also have functioned following the operation of the automatic recovery button 381 to maintain the aircraft on the heading it .had attained when the automatic recovery 'button was oper ated. The aircraft will now :be automatically maintained in its desired attitude on the heading stated.

The opera-tion of the lautomatic recovery arrangement will also be considered when the pilot desires that the .aircraft regain the desired attitude from an attitude that the plane has achieved lby operation of the automatic steering mechanism from a manual control which operates through said steering mechanism. For the purpose of manually controlling changes in attitude of the aircraft through the automatic steering mechanism there is provided the turn control potentiometer 12 and its operating knob 15. For :automatic control, the automatic steering mechanism is associated with the control sur faces by the operation of the engage button 351. Operation of the main engage button 351 completes a circuit .from battery 388, master button 40D, main bus 444 main disconnect 3|1, lead 445, Contact 35B of the anti-engage relay 359, switch arm ne, lead tee, main engage switch 354,1ead 45|, relay winding 3&5, to ground and to battery ground M8. The operation of the master engage relay 3655 elects the operation of the individual rudder, aileron and elevator engage relays to energize the servomotor brakes and to associate the ampliiier of each channel with its respective servomotor.

If the pilot wishes to turn the aircraft to the right, he operates the turn control knob 'l5 to move wiper le with respect to its resistor i3 whereby a signal is generated in network 'IB which is applied directly to the aileron amplifier 25. This signal is also applied from network Til through potentiometer il@ to the rudder ampliiler H25 causing the unbalance of the aileron and rudder amplifier networks. In response to this imbalance the respective ampliers cause the operation oi their servomotors whereby the ailerons and rudder are positioned and the follow up or re'balanoing wipers 33 and 133 are respectively positioned to again balance the networks. `The turn control knob 'l5 will also have caused the switch arm 23, Figure 2, to engage one or the other contacts 125, 25 whereby the circuit is completed from energized lead M5, lead i549, switch arm S'i, contact 38o, lead d5?, arm 423, contact li2t, or 525, caging relay coil M6, to ground and to battery ground 468.

The operation of the caging reiay M5 energizes the caging coil H2 of the caging mechanism whereby the directional gyro is centered and caged. With the gyro caged the wiper 6i) of the directional gyro aileron potentiometer 58 and the directional gyro rudder potentiometer it are unoperated. Under the applied ailerons and rudder the aircraft banks and turns. In response to the banking of the aircraft the vertical gyro 2l@ through its operating connection M will unbalanee the elevator network by the operation of wiper 259 and will also unbalance the aileron and rudder networks by the operation of wiper S3 of the vertical gyro banking potentiometer 6i. The signals from the vertical gyro as thus provided cause the aileron and rudder networks to become unbalanced whereby the aileron and rudder are moved back toward their normal position and the elevator network is unbalanced so that a slight amount of up elevator is applied. The aircraft will now continue in its 'banked turn unless the turn control knob l5 is restored to its original position.

Should the pilot desire that the plane be automatically returned to its original desired attitude he need merely to push without precise movement the automatic recovery button 381. When the automatic steering mechanism is associated with the control surfaces, the operation stated of the automatic recovery button 381 merely disconnects the primary winding 53 of transformer dii! from its supply and connects it to ground to deenergize the same and opens the circuit at contact 38E! and switch arm 373 for the caging coil M2. Other functions of the recovery relay had been effected by the main engage relay. The disengagement of switch arm 313 from contact 380 opens the circuit to caging relay H5 whereby the armature lll moves to its position shown completing a circuit through the uncaging coil [iii of caging mechanism lll.

Since the secondary winding i8 of the operated turn control potentiometer and the windings 52, I 52, 252 for the centering pctentiometers are now no longer energized, the centering potentiometer and the turn control potentiometer do not supply any control signal.

With the control signal from the turn control potentiometer l) no longer present in the aileron and rudder networks, they are unbalanced. The unbaiance present in these aileron and rudder networks due to the signal from the vertical gyro 2l@ because of the banked attitude causes the rudder and aileron amplier to operate their servomotors. This operation is such as to move the ailerons and rudder in an opposite direction from that in which they were originally positioned.

The amount of the bank of the aircraft decreases, and the vertical gyro Elu in response to the decrease in bank moves wipers 25S of the up elevator potentiometer 2S? and wiper e3 of the vertical gyro bank potentiometer back to their normal position. This results in unbalance of the aileron and rudder amplier networks whereby the ailerons and rudder are moved back toward their normal position. In addition, the elevator network has become unbalanced by the operation of wiper 253 toward normal position and the elevator is moved back toward its normal position.

rI'he operation is continuous in that in response to a decrease in bank the vertical gyro causes the control surfaces to be moved back to their normal position which is determined by the original attitude or the plane as governed by the automatic recovery potentiometers. When the aircraft has regained level position the potentiometer wipers S3 and El are in their normal position as determined by the attitude set up by the automatic recovery potentiometers. The aircraft is stabilized in this position by the vertical gyro and the heading oi the aircraft is maintained by the directional gyro 55 and the rate gyro 59.

It will be appreciated that in providing a single button control such as the automatic recovery button 382i which may be operated to regain the desired attitude or" the aircraft that such control will have a direct appeal to the pilot.

Under manual operation ci the controls, he may find himself in a cloud and unable to judge his attitude. Similarly, for other reasons, he is uncertain as to the proper manual operation of the control surfaces to regain a desired attitude. Cperation of the button 3S? however will automatically restore the aircraft to a preselected attitude.

On the other hand under automatic control with the turn control operated, his vision may have become impaired making him confused as to the manner in which the turn control knob i5 ought to be operated or to its extent of operation in order to right the aircraft. The operator of the push button 258i need not contemplate its extent or direction of adjustment which would be involved should he be required to operate the turn control knob d'5 in bringing the aircraft back to its desired attitude. Such lack of precise operation required of the automatic recovery button 353i as compared with the precise operation of the turn control knob W in order to regain the desired attitude of the aircraft is especially desirable where the pilot feels that he may become incapacitated from any cause as stated.

It is now apparent that I have provided a novel automatic steering mechanism which includes a single manually operable controller which may be operated in no particularly deterbodiment disclosed but only 'as definedY by the appended claims.

I` claim as, my invention:

1. Control apparatus for an aircraft having controlV surfaces4 'for 'controlling vsaid-aircraft about three-respectivelyperpendicular axes and manually operable means for positioning said lcontrol"surfaces, said apparatusA comprising:a powermeans adapted for association withfand for] operating each axis control `surfaceqa".'bal- 'anceable control means for each, powerrrreans, l

each ,control 'means including `apluralityfo'f A`signal generators and asigna-l""c z'c'imbining means; :attitude'responsive means"lmovable from` a normal position about one of said axes to operate a first signal generator in all of said control means; a second signal generator in each control means; positioning means for each second signal generator operated by each said control means while said respective power means is disasseciated from its control surface to maintain said control means in balanced condition during attitude changes while the control surfaces may be manually operated; means for associating each power means with its respective control surface to maintain the existing position of the aircraft irrespective of its attitude; a follow up third signal generator in each control means operated by each power means; and means for rendering ineffective each second signal generator in its operated position to thereby render each control means subservient to its first signal generator and return the craft to the normal position.

2. Control apparatus for an aircraft having a control surface said apparatus comprising: control surface power means adapted for association with said control surface control means for said power means, said control means including a balanceable electrical system having adjustable control devices for affecting its balance; attitude means for adjusting one control device; means operated by said control means while said power means is disassociated from said control surface for adjusting a second control device to rebalance said system to balance said electrical system during changes in the attitude of said aircraft; means for preventing the associating of said power means until said system is rebalanced by said second control device with said devices continuing to have effect on said electrical system; and means for associating said power means with said control surface irrespective of the balance of said electrical system and for rendering said second control device ineffective to affect said balance in its adjusted position.

3. Control apparatus for an aircraft having a manually or automatically operable control surface said apparatus comprising: power means which may be associated with said control surface; control means which may be associated 18 vwith said power meansfand including .a Abalanceable network having a plurality of lsignal generating devices; means -responsive to the attitude of the aircraft about `an axis for operating one generating device; means driven by saidV power :means for operating a second generating device; means-for operating a third adjustable device Yin said network to balance said network during l.craft attitudeLchanges with manual operation of said surface; operable means controlled by said network for associating said control means with .sai'dkpower means and for associating said power means withsaidcontrol surface only when said .network is balanced with said network effectively comprising =said;three generating devices; Aand further operable means* for rendering said thirdv generatingqdevice ineffective in said networkand .associating said control means with said power ymeans- -andsaid power means with said control surface irrespective of ff e unbalance of said network. Y

:.4. Control apparatus for an yaircraft having va control surface for controlling the -attitude of said-craft about an axis, said apparatus cornprising: manual means for operating directly said cont-rolisurface; `servo means for alternatively automatically operating'said control surface; voltage responsive controlrneans.; a network comprising a plurality of voltage producing devices for controlling said voltage responsive means; operating connections from said servo means to one of said devices for adjusting the same; motor means for adjusting a second of said devices; attitude means for adjusting a third of said devices; means for controlling said motor means from said voltage responsive means during manual operation of said control surface; means for transferring control by said potential responsive means from said motor means to said servo means; manually operable means for adjusting a fourth of said devices for changing the attitude of said craft about said axis during automatic operation; and means for rendering said manually operable device and said motor operated device ineffective in said network whereby the attitude of said craft conforms to the position of said attitude means.

5. Control apparatus for an aircraft having a manually or automatically adjustable control surface for controlling the attitude of the aircraft about an axis, said apparatus comprising: servo means adapted to be operatively connected with said control surface; voltage responsive control means including a network having a plurality of voltage producing devices connected in series; means responsive to movement of the aircraft about said axis for adjusting a first voltage producing device; manual means for adjusting a second voltage producing device in said network to select an attitude about said axis to be maintained automatically; motor means normally connected to said voltage responsive means being controlled thereby and adjusting a third voltage producing device in said network to maintain electrical balance in said network during craft attitude changes with said surface manually adjustable; and means for shifting connections of said control means from said motor means to said servo means and for associating said servo means with said control surface to automatically maintain craft attitude as determined by said three devices; and further means for rendering said motor operated voltage producing device and said manually operable voltage producing device ineffective in their adjusted positions in said network whereby said responsive means through said network solely determines the attitude of said craft.

6. Control apparatus for an aircraft having a control surface and manually operable means for positioning said control surface to change the attitude of said craft from datum about one axis, said apparatus comprising: surface power means normally disassociated from said surface but which may be associated with said control surface; operable control means for said power means including a balanceable electrical network having a plurality of signal producing devices each having two relatively movable parts for producing voltage signals proportional to the relative movement, for affecting the balance of said network, said network on unbalance causing control means operation; means responsive to the change in attitude of said aircraft from a datum about said axis for relatively moving the two parts of a rst control device in proportion to the magnitude of change in attitude to unbalance said network; a synchronizing motor operated by said control means while said power means is disassociated from said control surface to relatively move the parts of a second control device to rebalance said network to terminate control means operation; means for relatively moving the parts of a third control device by said power means;

apparatus engaging means for associating said power means with said control surface and also with said control means while said network is balanced to maintain thereafter said aircraft in said changed attitude as determined by the previous relative movement of the two parts of the second control device; and attitude changing means including disabling means for rendering said second control device with its two parts remaining relatively displaced ineffective in said network but with said power means associated with said control surface, to cause the network to be unaffected by the previous change in attitude l to thereby restore said aircraft to datum under the supervision of the first control device.

WILLIAM J. MCGOLDRICK.

References Cited in the file of this patent UNITED STATES PATENTS Young et al Oct. 9, 1951 

